I've got several custom widgets which are extended from WP_widget. Many of these have textarea fields. I'd like to be able to apply a special css class to certain of these textareas in order to convert them to rich text areas with a basic TinyMCE toolbar control.

How involved is this to do?

I'd like to implement a solution that inherits most or all of its code from the WP core and just piggyback off that.